The human arm constitutes a gripping device whose capabilities can only incompletely be reproduced by mechanical devices. There has, however, been an effort made to build manipulating devices for industrial robots which can make movements such as a man can make with his arm and hand. In some cases, it is even tried to design the manipulating device to be capable of carrying out tasks man can only handle with difficulties, as for example, motions which must be repeated with high precision.
A known manipulating device uses a rotatable support mounted on a stand. On this support a lever system with three pivotally connected members is swung. At the end of the last member a gripper or a tool is provided. The motion of the gripper within a vertical plane through the (usually vertical) axis of the rotatable support is produced by three drive units. The dirve unit for the first member is located on the support, the drive unit for the second member is located on the first member and the drive unit for the third member is located on the second member. A fourth drive unit produces swivelling of the lever system around the normally vertical support axis. This known manipulating device is very cumbersome in operation because the lever system must also carry the weight and bulk of the second and third drive units. Because of the weight of these drive units there is a tendency for flexing which may substantially affect the precision of positioning. It is not possible to obtain high positioning velocities because the mass of the accelerated parts is high so that it may be difficult to execute manipulation without exciting undesirable vibration.